It's funny because one of the OG draws to Steam back in the day was because Counter-Strike (et al) had the superior Valve Anti-Cheat (VAC) in Steam copies than the myriad of raw CD installs of HL1 plus the mods to run Counter-Strike.

This missing piece is sort of a fun "whatever happened to VAC and why hasn't it kept up with the times?"

It seems like Linux would be a good excuse to reinvest in VAC and make it a bigger competitor to the current favorites like Easy Anti-Cheat (EAC).